The present invention relates generally to position determination and, in particular, concerns to server-assisted position determination technology in a radio network.
Global Positioning System (GPS) receivers normally determine their position by computing relative times of arrival of signals transmitted simultaneously from a multiplicity of GPS (or NAVSTAR) satellites. These satellites transmit, as part of their message, both satellite positioning data as well as data on clock timing, so-called xe2x80x9cephemerisxe2x80x9d data. The process of searching for and acquiring GPS signals, reading the ephemeris data for a multiplicity of satellites and computing the location of the receiver from this data is time consuming, often requiring several minutes. In many cases, this lengthy processing time is unacceptable and, furthermore, greatly limits battery life in micro-miniaturized portable applications.
Another limitation of current GPS receivers is that successful operation is limited to situations in which multiple satellites are clearly in view, without obstructions, and where a good quality antenna is properly positioned to receive such signals. As such, they normally are unusable in portable, body-mounted applications, in areas where there is significant foliage or building blockage (e.g., urban canyons), and in in-building applications.
One known solution to this problem involves the use of a cellular telephone, integrated with a GPS receiver. A cellular link is established between the mobile GPS unit, or client, and a second, stationary, GPS receiver, which is associated with a second cellular unit and a computer processor, or server. The mobile GPS receiver takes what is referred to as a snapshot of the available satellite signals. That is to say, the mobile GPS receiver records a short duration of signals from as many satellites as are available in its line of sight. As described above, these signals are likely to be attenuated and fragmented, due to the location of the mobile GPS receiver, which may be in close proximity to buildings or foliage, etc.
According to one known method, described in U.S. Pat. No. 6,131,067, these fragmented signals are digitized, and transmitted, via a cellular link, from the client to the second GPS receiver and server. The second GPS receiver, meanwhile, is recording signals from GPS satellites within line of sight of its own antenna, which is a stationary mounted antenna, situated in a location where it receives unobstructed transmissions from the available satellites. The server associated with the second GPS receiver is then tasked with comparing the signals of the two receivers. By analyzing the fragmented signals from the mobile GPS receiver to the complete signals received by the second GPS receiver, the server can essentially xe2x80x9cfill in the blanksxe2x80x9d and complete the signals as received at the mobile GPS receiver. The server can then take those reconstructed signals and, using known methods, accurately determine the location of the mobile GPS receiver.
The amount of assistance afforded by the second GPS receiver or base station, can vary significantly. It may be as little as transmitting stored information regarding specific satellites, up to performing the matching process and signal analysis as previously described. In all cases however, the server-assisted location technology requires the use of a cellular link, or some other dedicated transmission medium such that a two-way communication link is continuously established between the client and server.
In other circumstances, a cellular telephone network is not available and radio communication is provided between parties. As those skilled in the art can appreciate, radio communication is intermittent with a single transmitter transmitting at a selected frequency and any receiver tuned to the selected frequency being capable of detecting the transmitted signals. When the transmitter completes transmitting, the selected frequency is available for use by any other transmitter. Thus, a particular frequency or channel is available for use by any transmitter. The server-assisted location technology described above cannot be implemented in a conventional two-way radio because radio communication, does not permit a dedicated two-way communication link. Therefore, it can be appreciated that there is a significant need for server-assisted location technology in a two-way radio system. The present invention provides this, and other advantages, as will be apparent from the following detailed description and accompanying figures.
A server-assisted position detection device comprises a client global positioning system (GPS) receiver circuit to receive satellite positioning signal data from GPS satellites. The satellite position data received by the client GPS receiver is insufficient to independently establish the location of the client GPS receiver. The client further includes a transmitter to transmit satellite data. A client carrier detection module is used to detect radio traffic on a selected radio frequency (RF) channel. A client transmit enable module enables the client transmitter when no radio traffic is detected on the RF channel.
A server receiver receives data from the client transmitter. A server coupled to the server receiver is configured to analyze the satellite data received by the server receiver. The server uses the received satellite data and additional satellite data to generate location information regarding the location of the client GPS receiver.
The location information may be used remotely or returned to the client unit. To return the location information to the client unit, the system may further comprise a client receiver to receive the location information and a server transmitter to transmit the location information to the client receiver. The server unit further comprises a server carrier detection module to detect radio traffic on an RF channel and a server transmit enable module to enable the server transmitter when no radio traffic is detected on the RF channel to thereby transmit the location information to the client receiver. In alternative embodiments, the client may further comprise a client user interface for displaying the location information. The client user interface may further comprise representation of a local map to indicate the location information.